Lifting boat trailers, per se, are generally well known, but they suffer several disadvantages. More specifically, such trailers operated by hydraulic systems are very expensive and complicated. Boat trailers having a front-mounted winch which applies a pulling force to the front end of the frame suffer from the disadvantages of requiring an unacceptably high force to be applied to the winch handle, causing bending of the frame members when such a high force is applied, and not being lowerable or collapsible to a sufficiently flat position to permit them to be driven underneath a pontoon boat sitting with its pontoons on the ground.
Lifting trailer s have also been disclosed in several U.S. patents. For example, U.S. Pat. No. 4,221,420 discloses a boat-and-car trailer having a first support assembly for the car and a second support assembly for the boat. Two pairs of pivotal scissor arms are secured to opposite sides of the first and second support assemblies and are hydraulically actuated to raise the boat support assembly from a collapsed position to a boat-supporting position. U.S. Pat. Nos. 4,286,800 and 4,406,477 disclose boat trailers having a collapsible boat-supporting structure, with the latter patent disclosing a winch and a cable pulley system which is used to raise a boat-supporting frame. U.S. Pat. No. 3,974,924 discloses a boat trailer having an aft cradle which provides mechanical leverage to assist in loading and unloading a boat. U.S. Pat. No. 4,637,770 discloses a pontoon boat trailer utilizing a winch and cable system for simultaneously applying a lifting force to the front and rear ends of a lifting frame pivotally attached by a parallelogram structure to a lower frame. U.S. Pat. No. 3,113,686, U.S. Pat. No. 4,318,632 and U.S. Pat. No. 4,365,923 further show the state of the art of lifting boat trailers.
It is to overcome the disadvantages of such prior structures that this invention is directed.